As Barack Obama prepares to vacate the Oval Office after two terms, he has earned an odd distinction: the United States has been at war every day of his tenure, a record unmatched in American history. The next president’s performance as commander in chief may well dwarf the importance of any domestic-policy position he or she takes. In fact, the central role of immigration and trade in the current presidential contest suggests that there is no longer any easy way of separating foreign from domestic policy. A serious consideration of the current state of the world, however, has been largely…